U.S. tornado outbreaks happen nearly every year, but outbreaks of this magnitude and the outbreak at the end of April 2011 are rare.

â€œA March tornado outbreak of similar scope to (the recent one) occurs roughly once a decade," according to Russell Schneider, the director of NOAAâ€™s Storm Prediction Center in Norman, Oklahoma.

This chart compares the number of tornado warnings during the April 2011 tornado outbreak and last week's storms.

Prior to April 2011, the U.S. last saw an outbreak of that magnitude in April 1974, when 148 tornadoes swept across 13 states, killing 330 people, and injuring 5,484. The outbreak on April 27 and 28, 2011, is the second deadliest outbreak in U.S.history, since records have been kept. It resulted in 320 deaths as 305 tornadoes swept across four states.

As surveys of the hard-hit areas are completed, the confirmed count could continue to rise. So far, this recent outbreak saw 128 reports of tornadoes across 12 states, with 45 of those tornadoes being confirmed.

This graphic shows the number of tornado reports associated with last week's outbreak.

These current statistics make March 2, 2012, one of the deadliest March days since 1994. If the death toll rises, this could be the worst March outbreak, which will not be confirmed until the National Weather Service completes its local damage assessments.

Given the severity of this recent outbreak, does this actually mean that we can expect another harrowing spring for tornadoes?

The U.S. winter of 2011-2012 was largely dominated by a La NiÃ±a event, which refers to abnormally cool temperatures in the Pacific Ocean, and that current La Nina is now weakening.

According to the Earth System Research Laboratory, research covering 1950-1992 found that La NiÃ±a years could lead to increased tornado activity for the Ohio River Valley and the Deep South. However, ESR says another study conducted over a longer period (1950-2003) found that neither theÂ frequency of tornado days nor those of violent tornado days is affected by El NiÃ±o.

So it is not clear whether a particular year will have more tornadoes, but this year's winter has been warmer, allowing the Gulf of Mexico to stay relatively warm.

The Gulf is where these storm systems get their main moisture supply, and warmer waters allow for greater amounts of that moisture to be evaporated into the atmosphere. When you couple that abundance of moisture with very warm temperatures ahead of a strong upper-level storm system, you get the perfect ingredients for an outbreak, according to the National Weather Service.

Devastating outbreaks in spring 2011 had already put people on high alert for the upcoming season.

There have been huge advances in tornado detection in recent years, and that allows National Weather Service forecasters to give the public greater lead times when issuing warnings. On days like last Friday, when tornadoes are everywhere, people are more alert to the weather situation and more likely to take shelter in case of danger.

But if this early start to the tornado season tells us anything, it is that warnings by themselves are not enough: Establishing a safety plan with your family can save precious time, and hopefully, precious lives.

People all across the country, and certainly those in tornado-prone areas, should review their family safety plans to ensure the most timely response during a tornado warning.

soundoff(184 Responses)

Ghabriel

Hi, this is great footage! I am a site eaoistigntvr for TORRO (The TORnado and storm Research Organisation) and Editor of The International Journal of Meteorology (IJMet) it'd be really great to have a chat with you about this event for our continuing research very very well done for capturing it on video! Please email me at if you are interested in telling us about the event!

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